An exit cavity was crucial to the polymerase activity of the early ribosome

The emergence of an RNA entity capable of synthesizing peptides was a key prebiotic development. It is hypothesized that a precursor of the modern ribosomal exit tunnel was associated with this RNA entity (e.g., "protoribosome" or "bonding entity") from the earliest time and played an essential role. Various compounds that can bind and activate amino acids, including extremely short RNA chains carrying amino acids, and possibly di- or tripeptides, would have associated with the internal cavity of the protoribosome. This cavity hosts the site for peptide bond formation and adjacent to it a relatively elongated feature that could have evolved to the modern ribosomal exit tunnel, as it is wide enough to allow passage of an oligopeptide. When two of the compounds carrying amino acids or di- or tripeptides (to which we refer, for simplicity, as small aminoacylated RNAs) were in proximity within the heart of the protoribosome, a peptide bond could form spontaneously. The growing peptide would enter the nearby cavity and would not disrupt the attachment of the substrates to the protoribosome or interfere with the subsequent attachment of additional small aminoacylated RNAs. Additionally, the presence of the peptide in the cavity would increase the lifetime of the oligopeptide in the protoribosome. Thus, subsequent addition of another amino acid would be more likely than detachment from the protoribosome, and synthesis could continue. The early ability to synthesize peptides may have resulted in an abbreviated RNA World.     

Oncogenic and mutagenic effects of UV in mammalian cells

Ultraviolet light is present in the solar system and can cause major biological effects. The potential cytotoxic, mutagenic, and carcinogenic effects of UV have been studied at cellular and molecular level. Using cultured mouse embryonic fibroblasts (C3H10T1/2), we investigated the induction of mutation and transformation by UV and/or X-rays. Studies were also done with normal human mammary epithelial cells for cell inactivation and mutation induction. Curvlinear dose-response curves were observed for mutation and oncogenic transformation. The interaction between UV and X-rays depends on the sequence of exposure. When UV was given following X-irradiation, there was an additive effect. When UV was given prior to X-irradiation, however, there was a synergistic effect for both cell inactivation and transformation. The basic lesion(s) important for somatic mutation and transformation remains to be determined, and the fundamental mechanism(s) of UV and ionizing radiation interaction remains to be elucidated.     

Digital Simulations of Effects of Two-Antenna Interference on Space Vehicle Guidance

This study determines through digital simulations the effects of two-antenna interference, defined as interference occurring at the ground guidance system antenna between the signals from two antennas located on, opposite sides of a space vehicle. It is demonstrated that errors due to interference during early booster flight are recovered from at booster cutoff; interference produced errors occurring shortly before cutoff are not recovered; and modulating the gain of one spaceborne antenna is beneficial to guidance in the interference region.     

The MESSENGER Spacecraft

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was designed and constructed to withstand the harsh environments associated with achieving and operating in Mercury orbit. The system can be divided into eight subsystems: structures and mechanisms (e.g., the composite core structure, aluminum launch vehicle adapter, and deployables), propulsion (e.g., the state-of-the-art titanium fuel tanks, thruster modules, and associated plumbing), thermal (e.g., the ceramic-cloth sunshade, heaters, and radiators), power (e.g., solar arrays, battery, and controlling electronics), avionics (e.g., the processors, solid-state recorder, and data handling electronics), software (e.g., processor-supported code that performs commanding, data handling, and spacecraft control), guidance and control (e.g., attitude sensors including star cameras and Sun sensors integrated with controllers including reaction wheels), radio frequency telecommunications (e.g., the spacecraft antenna suites and supporting electronics), and payload (e.g., the science instruments and supporting processors). This system architecture went through an extensive (nearly four-year) development and testing effort that provided the team with confidence that all mission goals will be achieved. Larry E. Mosher passed away during the preparation of this paper.